1. Field of the Invention
The invention relates generally to a method for processing sugar bagasse in a sugar cane processing plant. More particularly the invention is directed to a method for processing sugar bagasse in a manner which significantly increases energy output and an improved sugar cane processing plant therefor is also disclosed.
2. Description of the Prior Art
Sugar cane is a subtropical and tropical crop that prefers lots of sun and lots of water—provided that its roots are not waterlogged. Sugar cane can average 12 months to reach maturity, although time varies widely around the world, taking anywhere from 6 months to 24 months. Where sugar cane differs from many crops is that it regrows from the roots so the plant may grow through many cycles before it no longer regrows.
Sugar and fiber content also vary in sugar cane, without regard to source of origin. New varieties with early maturity, such as Cameroon sugar cane (low in sugar, high in fiber, normally used for animal feeds) is typically ground twice a year for the production of ethanol and electricity in agro-industrial regions.
Sugar cane is harvested by chopping down the stems while leaving the roots behind for regrowth potential. Harvest is usually conducted during the dry season and the length of the harvest may range from as little as 2.5 months up to 11 months.
Processing the sugar cane involves several stages, beginning with the extraction of the cane juice. In many processing plants, the cane is ground and crushed in a series of large roller mills. The number of mills varies depending on the amount of juice to be extracted and/or the grinding capacity needed. The sweet juice gushes out of the cane and the cane fiber remaining is pumped to a boiling house for the production of sugar, ethanol and/or sub-products, as known, and the cane fiber is then sent to and utilized as fuel for the boilers. In other processing plants, a diffuser is used.
The juice extracted at the mills, normally from first and second mills, is high in yield. The extracted juice is pumped to a boiling house, after dirt and solid impurities are removed from the juice. This cleaning process is known as purification of the juice. In the raw sugar industry, lime and heat are the agents almost exclusively used for this purpose, with a small amount of soluble phosphate generally being added into the process.
The extracted juice goes through a lime mixing system, with the heavy, thick lime mud created going to a conical bottom of a settling tank and the lighter cold, limed juice which flows along the top is pumped to the juice heaters. The heavy, thick lime mud from the conical bottom is washed out during periodic cleaning of the system. Thus a secondary system is necessary for continuous plant operation.
Pursuant to the above defined method, a sticky, brown sugar product is formed, which is further refined when it arrives in it country of destination. Additionally, since all the sugar cannot be removed from the juice, a sweet by-product, molasses, is created as well, which is turned into a cattle feed or is sent to a distillery where alcohol is made.
Bagasse is the fibrous residue remaining after the sugar cane is crushed to extract juice therefrom and is currently used as a renewable resource in the manufacture of pulp, paper products and building materials. For each 100 tons of sugar cane crushed, a sugar factory produces nearly 30 tons of wet bagasse. Historically, bagasse processing plants have had harsh working environments due to the pulp mill process. The plant also requires electricity and steam to run, both of which are generated using this bagasse fiber.
Bagasse has several possible uses including the possibility of burning it in large furnaces where much heat is released and used in turn to boil water to create high pressure steam. The steam generated drives a turbine to make electricity and to create low pressure steam for the sugar making process. A substantial impediment to wide scale use of bagasse is difficulty in depithing, a process wherein pith is separated from the bagasse fibers.
The traditional way of handling bagasse from the last mill is as follows: it is transported to boilers, with an excess of 10-15%, in a well balanced sugar processing plant being carried to a bagasse warehouse. When there is a lack of bagasse from the mills, the bagasse from storage is carried back to the boilers and by using a front-end loader it is either dumped into a reclaim hopper conveyor or directly into a floor level conveyor which carries it to boiler feeders. When the storage reserves become low, oil must be burned to maintain production.
In the present invention, pulverized bagasse is circulated back to the fiber fuel warehouse from the boilers, maintaining 70-75% of its capacity in reserve, with the reserve bagasse being stored a in dozen or so piles 40-50 feet high to protect it from heavy wind, rain such as that occurring during the rainy season. Each pile is covered with a stainless steel top and when any of the dozen piles in the storage system drops to a moisture content of approximately 30-40% by weight, the bagasse is pulverized and taken to the fiber fuel warehouse for further drying.
For back up of the bagasse reserve at the sugar plant, sub-systems operating all year in the region are provided, using identical technology to store the waste bagasse fibers, with it being trucked to the bagasse waste piles station.
As a power plant produces electricity, fossil fuel is typically used, such fuel contaminating the atmosphere. The power station or plant must also dump much low grade heat. Such dumping contributes to global warming. In the proposed cane sugar processing plant, bagasse fuel is renewable and the waste gas it produces, essentially CO2, is taken up by growing sugar cane. Also, the plant's use of low grade heat (called cogeneration) makes a well-run sugar cane estate environmentally friendly.
Considering the presently high price of oil, keeping production at low cost, and considering how harmful gases produced by the burning of oil are to the environment, seeking alternative sources of energy has become extremely important. New environmentally friendly sources of energy are believed to reduce global warming, as well as reducing dependence on foreign oil, and fossil fuel as sources of energy.
It will take years before 3rd world nations will be able to use new, more sophisticated technologies. Instead of waiting, the use of bagasse as a clean and renewable energy would be available, which bagasse could produce not only sugar, but also ethanol, sub-products, as well as producing electrical power. It could be a new start for prosperity for many underdeveloped countries.
Many research efforts have attempted to use bagasse as a renewable feedstock for power generation and for the production of bio-based materials. A primary fuel source for sugar mills is the main use for bagasse, which may be burned to produce sufficient heat energy to supply all the needs of a typical sugar mill, with energy to spare. To this end, a secondary use for this bagasse waste product is cogeneration, the use of a fuel source to provide both heat and energy. Both things are used in the mill, and excess electricity is created as well, which typically is sold to a public electricity grid.
A typical power plant facility uses bagasse and urban wood waste as fuel to generate enough energy to power its large milling and refining operations, as well as to supply renewable electricity. Such facility reduces dependence on oil by more than one million barrels of oil per year. Such facility thus saves approximately 10 of 12 months of oil dependency, also saving 80-85% in energy costs per year for the surrounding region of the plant, i.e., towns and cities associated with the raw sugar processing plant.
Ethanol produced from the sugar cane is, for example, a popular fuel for use in Brazil.
There are several known methods for using bagasse as a secondary product during the sugar cane processing. For example, a method for preparing and using a combustible fuel product using sweet sorghum is known. A sorghum variety high in sugar, high in biomass, and low in nitrogen is first processed to remove a majority of sugar therefrom.
The remaining lignocellulose residue, referred to as bagasse, is presently converted into combustible pellets or is alternatively stored for future pelletization. Storage is accomplished by first piling the bagasse on a hard surface. The bagasse is then compressed to form a compacted mass in the form of a pellet. Compression of the bagasse frees air trapped in the pile, hindering oxidative degradation by bacteria and other microorganisms.
Even though the above mentioned methods and technology presently used define a suitable approach for maximization of the natural resources used in a sugar cane processing plant, a method for processing bagasse in a more environmentally friendly, and more profitable, manner is still desired.